Widening the Latency Gap in Chelated Ruthenium Olefin Metathesis Catalysts

Abstract

The synthesis of novel sulfur-chelated ruthenium benzylidenes afforded latent catalysts with a wider range of activities and new isomeric forms. A ruthenium complex with a tridentate ligand displayed latency for even one of the most reactive ROMP monomers, dicyclopentadiene, while a room temperature latent trifluoromethyl-substituted thioether derivative was shown to be the most active sulfur-chelated precatalyst to date in several metathesis reactions at higher temperatures. These new complexes widen the spectrum of activity for this family of catalysts, enabling several practical applications and enhancing the understanding for the mechanisms of activation in strongly chelated ruthenium alkylidenes.

Initiation efficacy of halo-chelated cis-dichloro-configured ruthenium-based second-generation benzylidene complexes in ring-opening metathesis polymerization

“…In contrast, pre-initiators 6 and 7 gave poly9 with M n s of 62000 (PDI = 1.2) and 1.4). These results suggest that the trans isomers are in toluene energetically more favorable than in dichloromethane, which is in accordance with literature [26][27][28] and with calculations [15]. Further, it is quite obvious that the trans isomer is formed rapidly and is readily extracted from the chemical balance by entering the polymerization cycle.…”

“…As it is known, that the position of the cis-trans dichloro isomerization equilibrium is influenced by the nature of the solvent (high dielectric constant solvents favor the cis isomer) [26][27][28], we conducted a further test series in toluene, at that time at 80°C. Assumedly, 80°C is a temperature high enough to cancel out the influence of the energy for dissociation of the Ru-halogen bond and the initiation efficacy should be only dependent on the chemical balance of the isomerization reaction [13].…”

Remote control grubbs catalysts that modulate ring‐opening metathesis polymerizations

“…In 2011, Lemcoff and coworkers reported the synthesis of a photoactivated latent ROMP catalyst that was based upon a sulfur‐chelated Ru‐benzylidene complex (Fig. , 19 ) . Similar to the sulfur‐chelated analogs described above, this complex adopted a cis ‐dichloro conformation that rendered it inactive in olefin metathesis reactions at room temperature.…”

Ruthenium(IV)–Bis(methallyl) Complexes as UV‐Latent Initiators for Ring‐Opening Metathesis Polymerization

“…[28,29] These compounds do not show any ROMP activity up to 60 8C in the presence of cyclic olefins such as norborn-2-enes, 7-oxanorborn-2-enes and cis-cyclooctenes, however, they can be activated with UV-light and transformed into ROMP-active initiators. [29][30][31][32] Despite the fact that Ru IV complexes are well-known in coordination and organometallic chemistry, their use in catalytic reactions has been studied to a lesser extent than that of Ru 0 , Ru II and Ru III compounds. This is surprising, as the Grubbs-type initiators may be formally regarded as Ru IV -alkylidenes, though cyclic voltammetry (CV) suggests that their existence more closely resembles that of Ru II -carbene complexes (see the Supporting Information).…”